UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level

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1 UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level * * CHEMISTRY 9701/33 Advanced Practical Skills 1 October/November hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Give details of the practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. of a Data Booklet is unnecessary. Qualitative Analysis Notes are printed on pages 12 and 13. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Session Laboratory 1 2 Total This document consists of 13 printed pages and 3 blank pages and 1 insert. IB12 11_9701_33/FP [Turn over

2 2 1 You are to investigate how the rate of reaction between sodium thiosulfate and hydrochloric acid changes as the concentration of the sodium thiosulfate solution is varied. When aqueous sodium thiosulfate reacts with aqueous hydrogen ions present in an acid, a fi ne suspension of solid sulfur is formed in the solution. S 2 O 3 2 (aq) + 2H + (aq) S(s) + SO 2 (g) + H 2 O(l) The rate of reaction can be determined by measuring the time taken to produce a fi xed quantity of sulfur. The beaker containing a constant volume of reaction mixture is placed on the printed insert supplied. The time is recorded when the print is no longer visible through the suspension of sulfur. FA 1 is mol dm 3 sodium thiosulfate, Na 2 S 2 O 3. FA 2 is mol dm 3 hydrochloric acid, HCl. distilled water Read through the instructions carefully and prepare a table for your results on page 4 before starting any practical work. In each of the following experiments you will use varying volumes of FA 1 and distilled water and a fi xed volume of FA 2. The total volume of solution used will be constant. (a) Method Experiment 1 the measuring cylinder labelled A to transfer 50 cm 3 of FA 1 into a 250 cm 3 beaker. the measuring cylinder labelled B to measure 20 cm 3 of FA 2. Tip the FA 2 from measuring cylinder B into the beaker and immediately start timing. Stir the contents of the beaker once and place the beaker on the printed insert. View the print from directly above and through the solution in the beaker. Stop timing when the printed material on the insert is just no longer visible. Record the reaction time to the nearest second. (1000) Calculate and record the value of to 3 significant figures. (reaction time) Empty, rinse and dry the beaker.

3 3 Experiment 2 the measuring cylinder labelled A to transfer 40 cm 3 of FA 1 into the rinsed and dried beaker. the same measuring cylinder labelled A to transfer 10 cm 3 of distilled water into the same beaker. the measuring cylinder labelled B to measure 20 cm 3 of FA 2. Tip the FA 2 from measuring cylinder B into the beaker and immediately start timing. Stir the contents of the beaker once and place the beaker on the printed insert. View the print from directly above and through the solution in the beaker. Stop timing when the printed material on the insert is just no longer visible. Record the reaction time to the nearest second. (1000) Calculate and record the value of to 3 significant figures. (reaction time) Empty, rinse and dry the beaker. Experiments 3 5 Repeat the experiment using the following volumes of FA 1 and distilled water. Experiment 3 Experiment 4 Experiment 5 30 cm 3 of FA cm 3 of distilled water 20 cm 3 of FA cm 3 of distilled water 10 cm 3 of FA cm 3 of distilled water Experiment 6 When you have completed experiments 1 5, carry out one further experiment using a different volume of both FA 1 and distilled water. When you have completed all of your experiments, empty and rinse the beaker. [Turn over

4 4 Record the results for all six experiments in the space below. Your table should include columns for the following. experiment number volume of FA 1 volume of distilled water reaction time (1000) (reaction time) I II III IV V VI VII VIII IX X [11] XI (b) The rate of reaction can be represented by the following formula. (1000) rate = (reaction time) On the next page plot a graph of rate against the volume of FA 1. Start each of the axes at zero. Draw the line of best fit.

5 5 I II III IV V [5] [Turn over

6 6 (c) A student carried out the experiments in a 100 cm 3 beaker instead of a 250 cm 3 beaker. State and explain what effect this would have on the times recorded [2] (d) FA 1 is mol dm 3 Na 2 S 2 O 3. Calculate the initial concentration of Na 2 S 2 O 3 in the reaction mixture in Experiment 5. Show your working. The initial concentration of Na 2 S 2 O 3 in Experiment 5 = mol dm 3 (e) In your experiments, the volume of FA 1 represents the initial concentration of sodium thiosulfate in the reaction mixture. A text book states that the rate of reaction between aqueous sodium thiosulfate and hydrochloric acid is directly proportional to the concentration of sodium thiosulfate. your graph to decide whether the statement in the text book is correct or not. Explain your answer [2] [2]

7 7 (f) When viewing the insert through the solution it is diffi cult to judge the exact moment when the printed material just disappears. This uncertainty is different for each experiment and is greater for longer reaction times when the printed material disappears slowly. Complete the table below, assuming the uncertainties given. Experiment 1 Experiment 5 recorded reaction time / s uncertainty / s ± 2 ± 8 percentage uncertainty % % [1] (g) Complete the headings in the table below to record the volume of FA 1 (aqueous sodium thiosulfate), the volume of distilled water and the volume of FA 2 (hydrochloric acid). In the second row copy the volumes used in Experiment 3 from your table of results on page 4. In the following two rows suggest volumes of each of the reagents that could be used in two further experiments, Experiment 7 and Experiment 8, to investigate how the rate of reaction varies with a change in the concentration of the acid. Do not carry out these experiments. Experiment [2] [Total: 25] [Turn over

8 8 2 Qualitative Analysis At each stage of any test you are to record details of the following. colour changes seen the formation of any precipitate the solubility of such precipitates in an excess of the reagent added Where gases are released they should be identifi ed by a test, described in the appropriate place in your observations. You should indicate clearly at what stage in a test a change occurs. Marks are not given for chemical equations. No additional tests for ions present should be attempted. If any solution is warmed, a boiling tube MUST be used. Rinse and reuse test-tubes and boiling tubes where possible. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. Solutions FA 3, FA 4, FA 5 and FA 6 each contain one cation and one anion from those listed on pages 12 and 13. (a) Some cations interfere with tests for anions and have to be removed from the solution before the tests for anions present can be performed. One way in which this can be carried out is to precipitate the cation in the form of its insoluble carbonate. Carry out the following tests on both FA 3 and FA 5. test To 5 cm depth of solution in a boiling tube, add all of the sodium carbonate, Na 2 CO 3, from one of the tubes provided. observation FA 3 FA 5 Stir the mixture. Retain the mixture from FA 3 for use in (b). [4]

9 9 (b) Filter the mixture from FA 3 from (a) into another boiling tube. Ignore any colour in the fi ltered solution. Add 5 cm depth of dilute nitric acid. This removes any excess of carbonate ions. Carry out the following tests on the acidifi ed fi ltrate from FA 3. test To 2 cm depth of the acidifi ed fi ltrate from FA 3 in a test-tube, add 1 cm depth of aqueous silver nitrate, then observation add an excess of aqueous ammonia. [1] (c) Carry out the following test on FA 4. test To 1 cm depth of FA 4 in a test-tube, add 1 cm depth of FA 3, then observation add a few drops of starch solution. [2] [Turn over

10 10 (d) Carry out the following tests. observation test FA 3 FA 4 FA 5 FA 6 To 1 cm depth of solution in a test-tube, use a dropping pipette to add, a little at a time, 0.5 cm depth of aqueous sodium hydroxide, then add a further 2 cm depth of aqueous sodium hydroxide. To 1 cm depth of solution in a test-tube, use a dropping pipette to add, a little at a time, 0.5 cm depth of aqueous ammonia, then add a further 2 cm depth of aqueous ammonia. (e) The results from tests in (d) should enable you to identify either a single cation in a solution, or a pair of cations which have identical reactions with the reagents used. Identify any single ion that is present or suggest a pair of ions that may be present in each of the solutions. [4] solution cation(s) FA 3 FA 4 FA 5 FA 6 [2]

11 11 (f) Where you were unable to identify a single cation in (e), suggest a suitable reagent which would allow you to identify which cation is present in the solution. Do not carry out this test. The reagent to be used is... State the expected observations to identify the presence of each of the cations from the pair of ions you have given in (e). cation cation [1] (g) By considering the results of all your tests, enter one of the following responses in each of the boxes below. chloride bromide iodide no halide ion is present insufficient tests (have been performed to identify any halide ion) FA 3 FA 4 FA 5 [1] [Total 15] [Turn over

12 12 Qualitative Analysis Notes Key: [ppt. = precipitate] 1 Reactions of aqueous cations ion NaOH(aq) reaction with NH 3 (aq) aluminium, Al 3+ (aq) ammonium, NH 4+ (aq) barium, Ba 2+ (aq) calcium, Ca 2+ (aq) chromium(iii), Cr 3+ (aq) copper(ii), Cu 2+ (aq) iron(ii), Fe 2+ (aq) iron(iii), Fe 3+ (aq) lead(ii), Pb 2+ (aq) magnesium, Mg 2+ (aq) manganese(ii), Mn 2+ (aq) zinc, Zn 2+ (aq) white ppt. soluble in excess no ppt. ammonia produced on heating no ppt. (if reagents are pure) white ppt. with high [Ca 2+ (aq)] grey-green ppt. soluble in excess giving dark green solution pale blue ppt. green ppt. turning brown on contact with air red-brown ppt. white ppt. soluble in excess white ppt. off-white ppt. rapidly turning brown on contact with air white ppt. soluble in excess white ppt. no ppt. no ppt. grey-green ppt. blue ppt. soluble in excess giving dark blue solution green ppt. turning brown on contact with air red-brown ppt. white ppt. white ppt. off-white ppt. rapidly turning brown on contact with air white ppt. soluble in excess [Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(ii) chloride.]

13 13 2 Reactions of anions ion reaction carbonate, CO 3 2 chromate(vi), 2 CrO 4 (aq) chloride, Cl (aq) bromide, Br (aq) iodide, I (aq) nitrate, NO 3 (aq) nitrite, NO 2 (aq) sulfate, 2 SO 4 (aq) sulfi te, 2 SO 3 (aq) CO 2 liberated by dilute acids yellow solution turns orange with H + (aq); gives yellow ppt. with Ba 2+ (aq); gives bright yellow ppt. with Pb 2+ (aq) gives white ppt. with Ag + (aq) (soluble in NH 3 (aq)); gives white ppt. with Pb 2+ (aq) gives cream ppt. with Ag + (aq) (partially soluble in NH 3 (aq)); gives white ppt. with Pb 2+ (aq) gives yellow ppt. with Ag + (aq) (insoluble in NH 3 (aq)); gives yellow ppt. with Pb 2+ (aq) NH 3 liberated on heating with OH (aq) and Al foil NH 3 liberated on heating with OH (aq) and Al foil; NO liberated by dilute acids (colourless NO (pale) brown NO 2 in air) gives white ppt. with Ba 2+ (aq) or with Pb 2+ (aq) ( dilute strong acids) SO 2 liberated with dilute acids; gives white ppt. with Ba 2+ (aq) (soluble in excess dilute strong acids) 3 Tests for gases gas ammonia, NH 3 carbon dioxide, CO 2 chlorine, Cl 2 hydrogen, H 2 oxygen, O 2 sulfur dioxide, SO 2 turns damp red litmus paper blue gives a white ppt. with limewater (ppt. dissolves with excess CO 2 ) bleaches damp litmus paper pops with a lighted splint relights a glowing splint test and test result turns acidifi ed aqueous potassium dichromate(vi) from orange to green

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16 16 BLANK PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level

*0974901356* UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level CHEMISTRY 9701/31 Advanced Practical Skills 1 May/June 2013